Alkyltin Sulfanyl Mercaptocarboxylates Having Terminal Thiol Groups

ABSTRACT

An alkyltin compound of specified formula which has utility as an excellent stabilizer for a halogen-containing resin. The alkyltin compound has from 1-3 terminal thiol groups.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to alkyltin thermal stabilizers forhalogen-containing resin compositions. More particularly, the presentinvention relates to alkyltin sulfanyl mercaptocarboxylates having fromone to three terminal thiol groups and which are suitable for thermalstabilization of polyvinyl compositions.

2. Description of the Prior Art

British Patent Specification No. 866,484 generically discloses alkyltinsulfanyl derivatives having terminal thiol groups, which are said tostabilize vinyl resins against the degradative effects of both heat andlight. However, no experimental data is provided to quantify theseclaims for any of these compounds.

Non-thiol terminated alkyltin stabilizers are also known. For example,dimethyltin bis S,S (2-ethylhexanol thioglycolate) and di-n-butyl bisS,S (2-ethylhexanol thiolglycolate) are both commercially available. Oneof the most effective thermal stabilizers is a blend of dimethyltin bisS,S (2-ethylhexanol thioglycolate) and methyltin tris S,S,S(2-ethylhexanol thioglycolate). These compounds are also commerciallyavailable.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to an alkyltin compoundhaving the formula:

(R)_(x)Sn[—S—(CH₂)_(y)—COO—CH₂—CH₂—OOC—(CH₂)_(y)—SH]_(4-x)

wherein:

R is a C₁₋₃ alkyl group;

x is equal to 1 or 2;

y is equal to 1 or 2.

These organotin compounds may be generally described as condensationproducts of organotin derivatives (such as oxides and chlorides) anddimercaptoacid esters of ethylene glycol.

In a second aspect, the present invention relates to a composition whichincludes a halogen-containing resin and an alkyltin compound asdescribed above in an amount effective to stabilize the resin againstelevated temperatures, UV light, oxidation and high shear forces.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of yellowness index of sample chips taken at varioustimes during a heat stability test. The graph illustrates the improvedcolor stability of a rigid PVC formulation containing the new tinstabilizer in comparison to control formulations containing otherorganotin compounds present at the same tin level.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The alkyltin compounds of Formula 1 preferably have methyl groups for R.

Alkyltin compounds which come within Formula I and which areparticularly preferred include dimethyltin bis(1,2-ethanedithioglycolate), monomethyltin tris(1,2-ethanedithioglycolate),dimethyltin bis(1,2-ethane dimercaptopropionate), monomethylintris(1,2-ethanedimercaptopropionate) and mixtures thereof.

Those of ordinary skill in the art will recognize the alkyltin compoundsof the present invention may be prepared via several synthetic routes.In a preferred embodiment, these alkyltin compounds may be convenientlysynthesized using a two-reaction procedure which employs readilyavailable reactants. First, a dithiol ester is prepared byesterification of ethylene glycol with a thioacid in a molar ratio of1:2 in the presence of a suitable catalyst. It is preferred to use aslight excess (3-5%) of thioglycolic acid. Suitable thioacids includemercaptoacetic acid and mercaptopropionic acid. Appropriate catalystsinclude but are not limited to p-toluene sulfonic acid and methanesulfonic acid.

The esterification reaction may be performed with or without a solventat an appropriate temperature, for example, 130-150° C. Water formedduring the reaction is removed by conventional methods.

The resulting dithiol ester may be neutralized with an appropriate basesuch as sodium bicarbonate or potassium carbonate, purified by filteringsalt residues and stripped under vacuum to remove moisture, preferablyat an elevated temperature such as, for example, 60-80° C.

In the second stage of the synthesis, the dithiol ester is reacted withan appropriate tin-containing reactant, for example an alkyltin chlorideor alkyltin oxide, at the following molar ratios: for dialkyltinderivatives S:Sn>1.5 and for monoalkyltin derivatives S:Sn>1.0. Theresulting alkyltin compound thus contains both Sn—S bonds and free,terminal thiol groups.

The alkyltin compounds of the present invention impart superior thermalstability to halogen-containing resins. Such resins include polyvinylchloride (PVC), polyvinyl bromide, polyvinylidene chloride, copolymersof vinyl chloride and vinyl acetate, copolymers of vinyl chloride andvinylidene chloride, copolymers of vinyl chloride and acrylonitrile,copolymers of vinyl chloride and maleic or fumaric esters and copolymersof vinyl chloride and styrene.

An effective amount of the alkyltin compound is an amount which makesthe halogen-containing resin more resistant to discoloration than theresin per se. Generally, an effective amount will range from 0.5 to 1.50parts stabilizer per hundred parts resin, and will depend on thespecific resin and alkyltin compound, as well as the degree of thermalstabilization desired. A preferred amount of alkyltin compound is from0.8 to 1.2 parts stabilizer per hundred parts resin.

The alkyltin compound may be added to the halogen-containing resin usingtechniques and apparatus well known to those of ordinary skill in thisart. Generally, the resin may be mixed with the stabilizer in a highspeed mixer for 30-90 seconds to thoroughly disperse the alkyltincompound throughout the resin.

The halogen-containing resin may also contain known additives as long astheir presence does not materially degrade the thermal stabilityimparted by the alkyltin compounds of the present invention. Suchadditives include, without limitation, lubricants, fillers, pigments,flame retardants, UV absorbers, impact modifiers and processing aids.These additives may be added to the resin using techniques and apparatuswell known to those of ordinary skill in this art.

Suitable lubricants include calcium stearate, montan wax, fatty acidesters, polyethylene waxes; chlorinated hydrocarbons, glycerol estersand combinations thereof.

Suitable fillers include titanium oxide, calcium carbonate, kaolin,glass beads, glass fibers, talc, wood flour and mixtures thereof.

Suitable pigments include azo pigments, phthalocyanine pigments,quinacridone pigments, perylene pigments, diketopyrrolopyrrole pigmentsand anthraquinone pigments.

Suitable flame retardants include antimony oxide, molybdates, boratesand hydroxystannates.

EXAMPLES

The following Examples illustrate the practice and advantages ofspecific embodiments of the invention. The Examples are not intended tolimit the invention in any manner whatsoever.

Example 1 Synthesis of dimethyltin bis(1,2-ethane dithioglycolate)

62 g ethylene glycol was reacted with 191.2 g thioglycolic acid (TGA) inthe presence of 1 g p-toluenesulfonic acid (p-TSA) at 110-150° C. Over aperiod of 5 hours, 34 g water was collected (theory water 36 g). Thebatch was neutralized with 5 g K₂CO₃ and filtered to yield 214 g ofclear product. The acid value after neutralization was 0.051 meq/g.Mercaptan value by iodine titration was 28.74%. Gas chromatographicanalysis showed no ethylene glycol and 12.6% mono-thioglycolate and 80%di-thioglycolate.

100.7 g of the di-thioglycolate (1,2-ethane dithioglycolate) was reactedwith 50.13 g dimethyltin dichloride dissolved in 150 ml water. Thereaction mix was neutralized to pH 6.5 using ammonium hydroxidesolution. The crude product was separated from the aqueous phase andstripped at 80° C. and 2-5 mm Hg for 2 hours using a Buchi RotovaporR-134 evaporator. The product was filtered hot to remove traces ofresidual salts to yield 104 g of the clear product. Analysis: sulfurfound 22.34%, calculated 22.62; tin found 20.75%, calculated 20.85%.

Corresponding dimethyltin sulfanyl mercaptocarboxylates prepared from1,3-propylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol,respectively, and which were prepared in analogous manner, were used ascontrols.

Example 2 Evaluation of Color Stability

Rigid PVC formulations were prepared using the stabilizer of Example 1,the control stabilizers derived from diols of higher (than ethyleneglycol) molecular weight and commercially available alkyltinstabilizers, such as dimethyltin-bis(2-ethylhexylthioglycolate) (Mark1982), dibutyltin-bis(2-ethylhexylthioglycolate) (Mark 292S), and ablend of monomethyltin-tris(2-ethylhexylthioglycolate) withdimethyltin-bis(2-ethylhexylthioglycolate) (Mark 1900). The tin contentin the formulations was the same for all samples. Each PVC compound testsample was placed into a Brabender mixer operated at 190° C. and 65 RPM.Sample chips were taken every three minutes. Fusion time was about thesame for all samples.

Color stability was determined from sample chips using a Hunter Labcolorimeter measuring Yellowness Index (YI) (lower YI signifies lesserdiscoloration as a result of thermal decomposition and, therefore,superior thermal stabilization). See Table 1 and FIG. 1.

TABLE 1 Yellowness Index of PVC and analytical data on heat stabilizersMark Mark Mark 1,3-propanediol 1,4-CHDM EG 1,4-BG Time, min. 1900 1982292S derivative derivative derivative derivative  3 4.18 4.35 5.91 4.496.00 3.59 5.72  6 6.28 7.84 11.46 7.29 8.77 5.99 8.31  9 8.09 9.96 14.298.93 10.97 7.93 9.76 12 12.55 16.13 19.78 13.01 15.84 11.21 15.29 1520.69 33.30 34.03 21.37 26.21 18.41 25.12 Stabilizer Tin content, %19.40 19.67 18.08 18.65 15.62 20.85 19.00 Stabilizer added, phr 1.201.18 1.29 1.25 1.49 1.12 1.23 Tin amount added, phr 0.23 0.23 0.23 0.230.23 0.23 0.23 Note: “1,3-propanediol derivative” is dimethyl bis(1,3-propane dithioglycolate); “1,4-CHDM derivative” is dimethyltinbis(1,4-cyclohexane dithioglycolate); “EG derivative” is dimethyltin bis(1,2-ethane dithioglycolate); and “1,4-BG derivative” is dimethyltinbis(1,4-butane dithioglycolate). “Initial color hold” refers toyellowing resistance during the first 3 to 10 minutes of the Brabendercolor stability test. Monoalkyltin stabilizers are known to provide anexcellent initial color-hold. “Long term heat stability” refers toyellowing resistance at sample times greater than 10 minutes in theBrabender color stability test. Dialkyltin stabilizers are known toprovide superior long-term heat stability.

Blends of the monoalkyltin and dialkyltin moieties provide the mostefficient balance of both initial color-hold and long-term heatstability. One such blend is a mixture of monomethyltintris-(2-ethylhexylthioglycolate) and dimethyltinbis-(2-ethylhexylthioglycolate), which is commercially available fromCrompton Corporation under the tradename Mark 1900.

Added at the same tin content, the dimethyltinbis(1,2-ethanedithioglycolate) stabilizer of the present inventionachieved an initial color stability similar to that of the Mark 1900blend, as measured by yellowness index (from 3 to about 10 minutes inthe Brabender test; see Table 1 and FIG. 1). In other words, thedimethyltin bis(1,2-ethanedithioglycolate) stabilizer was unexpectedlyeffective in initial color stabilization despite the absence of amonoalkyltin moiety in its composition.

The dimethyltin bis(1,2-ethanedithioglycolate) stabilizer also exhibitedsuperior long-term heat stability in comparison to the Mark 1900 blend,as demonstrated by the yellowness index curves from 10-15 minutes duringthe Brabender color stability test.

Although the present invention has been described in great detail withrespect to preferred forms, many changes and variations are possible andwill be apparent to those skilled in the art after reading the foregoingdescription. It is therefore to be understood that the present inventionmay be practiced otherwise than as specifically described herein withoutdeparting from the spirit and scope thereof.

1. An alkyltin compound of Formula 1:R_(x)—Sn[—S—(CH₂)_(y)—COO—CH₂—CH₂—OOC—(CH₂)_(y)—SH]_(4-x) wherein: R isa methyl group; x is equal to 2; and y is equal to
 1. 2. (canceled) 3.(canceled)
 4. A composition comprising a halogen-containing resin and analkyltin compound of claim 1 in an amount effective to stabilize theresin against elevated temperatures.
 5. The composition of claim 4,wherein said halogen-containing resin is a member of the groupconsisting of polyvinyl chloride, polyvinyl bromide, polyvinylidenechloride, copolymers of vinyl chloride and vinyl acetate, copolymers ofvinyl chloride and vinylidene chloride, copolymers of vinyl chloride andacrylonitrile, copolymers of vinyl chloride and maleic or fumaric estersand copolymers of vinyl chloride and styrene.
 6. The composition ofclaim 4, wherein said effective amount is within a range of from 0.5 to1.8 parts stabilizer per hundred parts resin.
 7. The composition ofclaim 6, wherein said range is from 0.8 to 1.2 parts stabilizer perhundred parts resin.
 8. The composition of claim 5, further comprisingat least one additive selected from the group consisting of lubricants,fillers, pigments, flame retardants, UV absorbers, impact modifiers andprocessing aids.
 9. The composition of claim 8, wherein said lubricantsare selected from the group consisting of calcium stearate, montan wax,fatty acid esters, polyethylene waxes, chlorinated hydrocarbons,glycerol esters and combinations thereof.
 10. The composition of claim8, wherein said fillers are selected from the group consisting oftitanium oxide, calcium carbonate, kaolin, glass beads, glass fibers,talc, wood flour and mixtures thereof.
 11. The composition of claim 8,wherein said pigments are selected from the group consisting of azopigments, phthalocyanine pigments, quinacridone pigments, perylenepigments, diketopyrrolopyrrole pigments and anthraquinone pigments. 12.The composition of claim 8, wherein said flame retardants are selectedfrom the group consisting of antimony oxide, molybdates, borates andhydroxystannates.
 13. A method for preparation of the alkyltin compoundof claim 1, comprising i) esterifying ethylene glycol with a thioacid ina molar ratio of 1:2 in the presence of a suitable catalyst to produce adithiol ester; and ii) reacting said dithiol ester with a tin-containingreactant at the following molar ratios: for dialkyltin derivativesS:Sn>1.5.
 14. The method of claim 13, wherein said tin-containingreactant is an alkyltin chloride or alkyltin oxide.
 15. A method ofstabilizing initial color of PVC consisting of adding to the PVC about1.1 phr of dimethyltin bis(1,2-ethane dithioglycolate), wherein the PVChas a yellow index of about 3.6 at 3 minutes.
 16. The method of claim15, wherein the PVC has a Yellow index of about 6 at 6 minutes.
 17. Themethod of claim 16 wherein the PVC has a yellow index of about 7.9 at 9minutes.